Regional Summary The Green River basin continues show variability in water supply outlook conditions. While the entire basin has received normal to above normal season precipitation, snowpack ranges from below average to above average.

Despite above average precipitation in February, and near average seasonal precipitation for the water year, snow pack remains below average at 85 percent of the conditions on March 1st. Forecast for points in the Upper Green are lower and reflect the very dry soil condition upstream of Flaming Gorge. Model soil moisture states range from 60% to 15% of average for early March. This carryover from many years of below average runoff is not included in statistical guidance, but is responsible for a significantly lower guidance value from ESP. This is the NWS preferred values. Through the coordination process this was countered by higher NRCS preferred values. As a result, the majority of coordinated forecasts were not changed in the Upper Basin from February 1st.

The outlook for spring runoff in the Yampa and White continues to be above average. February precipitation was nearly 175% of average and brought the snowpack from 110% of average to nearly 115 % of the March 1st average. Model soil moisture conditions in the Yampa and White are near average and suggest a much more favorable melt scenario than in the Upper Green. Meteorologic models indicate some storm activity through the middle of the month which should preserve and increase snowpack.

Throughout February, snowpack continued to build throughout the Duchesne River Basin. Seasonal precipitation is near 130% of normal. In the headwaters, soil moisture conditions are near average for March 1st. All of these factors combine to indicate a potentially above average runoff for 2007.

Similar to the Yampa and Duchesne basins, February precipitation was near 170 percent of average with seasonal precipitation now 135% of average. Lower than normal accumulation amounts at some stations in the latter half of February resulted in a slight decrease in the March 1st percent of average snowpack. However, conditions still indicate that water supply should be near to above average for points within the Price, and San Rafael drainages.

Differences between the full period forecasts and the residual forecasts may not exactly equal the actual observed volumes due to rounding conventions (see Definitions section).

10% exceedance forecast: Given the current hydrometeorological conditions, i.e current snowpack, soil moisture and streamflow, the volume that has a 10% chance of being exceeded. Previously referred to as "Reasonable Maximum Forecast".

50% exceedance forecast: Given the current hydrometeorological conditions, i.e current snowpack, soil moisture and streamflow, the volume that has a 50% chance of being exceeded. Previously referred to as "Most Probable Forecast".

90% exceedance forecast: Given the current hydrometeorological conditions, i.e current snowpack, soil moisture and streamflow, the volume that has a 90% chance of being exceeded. Previously referred to as "Reasonable Minimum Forecast".

Acre-Foot (af): The volume equal to one acre covered one foot deep (43,560 cubic feet). See kaf below.

Average: The arithmetic mean. The sum of the values divided by the number of values. Values from 1971-2000 are used for this publication.

Categories: Much Above Average=Greater than 130%, Above Average=111-130%, Near Average=90-110%, Below Average=70-89%, Much Below Average=Less than 70%.

CBRFC: Colorado Basin River Forecast Center.

Forecast Period: The period from April 1 through July 31, unless otherwise noted.

kaf: Thousand Acre-Feet. See Acre-Foot above.

Inflow: The volume of water that flows into a reservoir or lake.

Median: The middle value of an ordered set of values. Half of the values are higher and half of the values are lower. When the set contains an even number of values the median is the average of the two middle numbers.

NOAA: National Oceanic and Atomospheric Administration.

NWS: National Weather Service.

Water supply forecasts take into consideration present hydrometeorological conditions and use average basin temperatures and precipitation for the forecast period. As the forecast season progresses, a greater portion of the future hydrologic and climatic uncertainty becomes known and monthly forecasts become more accurate. For more information on the tools we use, consult Water Supply Forecasting Tools.

Volume forecasts represent adjusted flows; that is, observed flows with upstream water use taken into account. Adjusted flows will closely approximate natural or unimpaired flows. However, not all upstream diversions or impoundments are measured or quantifiable. For specific adjustments used with each forecast point, consult the Guide to Water Supply Forecasting.

The Water Supply Outlook is issued monthly January through May by the Colorado Basin River Forecast Center. It represents a coordinated effort between the National Weather Service, Natural Resources Conservation Service, Bureau of Reclamation, U.S. Geological Survey and local water district managers.

Note: Data used in this report are provisional and are subject to revision.

For more information, or to be included on the mailing list, please contact:

Colorado Basin River Forecast Center
2242 W North Temple
Salt Lake City, UT 84116
(801) 524-5130
www.cbrfc.noaa.gov